Radiation resistant steel



Jan. 28, 1964 H. J. KIRSCHNING 3,119,537

RADIATION RESISTANT STEEL Filed Oct. 20. 1960 IN TOR. kw 17-44,,-

United States Patent 3,119,687 RADIATION RESISTANT STEEL Hans Joachim Kirschning, Duisburg, Germany, assignor to Klockner-Werke A.G., Duisburg, Germany Filed Oct. 20, 1960, Ser. No. 63,041 Claims priority, application Germany Oct. 22, 1959 5 Claims. (Cl. 75-420) The present invention relates to steel. More particularly, the present invention is concerned with radiation resistant steel and with structural elements formed thereof.

Structural elements which are exposed to radiation, such as elements which form parts of atomic reactors, are frequently exposed to high degrees of radiation. For instance, the steel elements of atomic reactors of the high pressure-steam type will be exposed to temperatures higher than 250 C. and pressures higher than 200 atmospheres, whereby water in the form of normal, heavy and heaviest water or as a mixture of Water containing various isotopes of hydrogen may be present in its liquid as well as in its gaseous phase. Furthermore, such structural elements of atomic reactors are attacked by neutron radiation.

It has been found that the materials of such structural elements which up to now were available do not fully satisfy the demands made by the above discussed conditions. Particularly, it is one of the disadvantages of conventional materials of such structural element that even very small portions thereof which by mechanical or other influences are separated from the structural element and are carried away, for instance, with the cooling agent, will cause a very serious danger of radio-active contamination outside the reactor. Furthermore, the useful life span of such structural elements of atomic reactors and the like made of conventional materials is considerably reduced due to the effect of exposure to neutron radiation.

It is therefore an object of the present invention to provide a material and structural elements which will not be subject to the above discussed difficulties and disadvantages.

It is a further object of the present invention to provide a steel alloy capable of withstanding radiation without causing the above discussed difficulties.

Other objects and advantages of the present invention will become apparent from a further reading of the description and of the appended claims.

With the above and other objects in view, the present invention comprises an austenitic steel containing up to 0.04% carbon and between 0.0001% and 0.05% of at least one rare earth selected from the group consisting of cerium, praseodymium and neodymium.

According to one preferred embodiment of the present invention, the same comprises in an atomic reactor, in combination, structural elements including a pressure boiler, sheathing of the core members, conduits for the cycling of the primary heat exchange medium, heat exchanger, and pump for cycling the heat exchange medium, the structural elements consisting of austenitic steel consisting essentially of iron and between 17% and 19% chromium, between 7% and 11% nickel, between 0.3% and 0.6% manganese, between 0.35% and 0.4% silicon, between 0.05% and 0.15% molybdenum, between 0.03% and 0.04% carbon, between 0.01% and 0.02% phosphorus, between 0.005% and 0.007% sulfur and between 0.0001% and 0.05% of at least one rare earth selected from the group consisting of cerium, praseodymium and neodymium.

Surprisingly, it has been found that low-carbon austenitic steels containing between 0.0001% and 0.05 of the rare earths mentioned above, will substantially reduce and in many cases completely eliminate the above dis- Patented Jan. 28, 1964 cussed difiiculties occuring when steel elements are exposed to atomic radiation.

It is important to note, that one of the essential requirements of the present invention is that the total amount of carbon in the steel must not exceed 0.04%. This is required in order to prevent the added rare earths quantities from entering into a stable chemical combination with the carbon content of the steel. It is an essential feature of this invention that the rare earth alloy metals are dissolved in the austenitic steel without entering into any combination with the carbon content of the steel. Probably the advantages of the invention are due to the fact that the rare earths metals are fully available as protecting elements against corrosion and radiation attacks instead of stabilizing steel by forming carbides. The quantity of the rare earths must be within the range of 0.000l% and 0.05 since on the one hand lower proportions than 0.0001% will not be sufliciently effective, on the other hand, proportions of more than 0.05 of rare earths Will cause excessive brittleness of the steel. Within the range of 0.0001% and 0.05 increased proportions of rare earths will increase the effectiveness of protection against atomic radiation while increasing the brittleness only within tolerable limits. The exact proportion of rare earth in the steel alloy will therefore depend on the degree of radiation and radiation hazard involved and on the permissible degree of brittleness of the steel member.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

The figure is a schematic illustration of an atomic reactor.

Referring now to the drawing, it is noted that reactors of the pressure or boiling water type which are operated With aqueous solutions are to a large degree built with steel sheathings and structural elements of steel. These elements include pressure boiler 1, the sheathing 2 of the fuel or core element, the conduits 3 for the primary heat exchange cycle, pump 4 which is operatively associated with conduits 3 and heat exchanger 5.

As noted further above, the carbon content of the austenitic steel according to the present invention must not exceed 0.04%, and the proportion of one or more of the rare earths mentioned above, must be between a minimum of 0.0001% and a maximum of 0.05 All percentage figures given herein are percent by 'weight. of the entire steel composition. The other constituents of the austenitic steel preferably will be within the ranges indicated in Table I.

Table 1 Percent Percent C 0.03-0.04 Si 0.35-0.4 Mn 0.3-0.6 P 0010-0020 S 0.005-0.007 Mo 0.05-015 Cr 17.0019.00 Ni 700-1100 At least one of Ne, Pr and Ce in a total quantity of between 0.0001% and 0.05 the balance iron and impurities as usually found in such steel.

Table 11 Percent Percent C 0.035 Si 0.36 Mn 0.4 P 0.015 S 0.005 Cr 18.00 Ni 10.00 Mo 0.07 Ce 0.015

3 Table III Percent Percent C 0.03 Si 0.39 Mn 0.5 P 0.011 S 0.006 Cr 17.00 Ni 11.00 Mo 0.12 Pr 0.009

Table IV Percent Percent C 0.04 Si 0.38 Mn 0.6 P 0.01 S 0.006 Cr 19.00 Ni 8.00 M 0.06 Ce 0.01 Pr 0.005

Table V Percent Percent C 0.03 Si 0.39 Mn 0.55 P 0.015 S 0.005 Cr 18.00 Ni 8.00 Mo 0.05 Ce 0.005 Pr 0.01 Ne 0.005

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended Within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In an atomic reactor a structural element adapted to withstand neutron radiation and consisting essentially of an austenitic steel consisting essentially of iron and between 17% and 19% chromium, between 7% and 11% nickel, between 0.3% and 0.6% manganese, between 0.35% and 0.4% silicon, between 0.05% and 0.15% molybdenum, between 0.03% and 0.04% carbon, between 0.01% and 0.02% phosphorus, between 0.005% and 0.007% sulfur and between 0.000l% and 0.05% of at least one rare earth selected from the group consisting of cerium, praseodymium and neodymium.

2. In an atomic reactor a structural element adapted to withstand neutron radiation and consisting essentially of an austenitic steel consisting essentially of iron and between 17% and 19% chromium, between 7% and 11% nickel, between 0.3% and 0.6% manganese, between 0.35% and 0.4% silicon, between 0.05% and 0.15% molybdenum, between 0.03% and 0.04% carbon, between 0.01% and 0.02% phosporus, between 0.005% and 0.007% sulfur and between 0.000l% and 0.05% of neodymium.

3. In an atomic reactor a structural element adapted to withstand neutron radiation and consisting essentially of an austenitic steel consisting essentially of iron and between 17% and 19% chromium, between 7% and 11% nickel, between 0.3% and 0.6% manganese, between 0.35% and 0.4% silicon, between 0.05% and 0.15% molybdenum, between 0.03% and 0.04% carbon, between 0.01% and 0.02% phosphorus, between 0.005% and 0.007% sulfur and between 0.0001% and 0.05% of cerium.

4. In an atomic reactor a structural element adapted to withstand neutron radiation and consisting essentially of an austenitic steel consisting essentially of iron and between 17% and 19 chromium, between 7% and 11% nickel, between 0.3% and 0.6% manganese, between 0.35% and 0.4% silicon, between 0.05% and 0.15% molybdenum, between 0.03% and 0.04% carbon, between 0.01% and 0.02% phosphorus, between 0.005% and 0.007% sulfur and between 0.0001% and 0.05% of praseodymium.

5. In an atomic reactor, a structural element adapted to withstand neutron radiation and consisting essentially of an austenitic steel consisting essentially of iron and between 17% and 19% chromium, between 7% and 11% nickel, between 3% and 0.6% manganese, between 0.35% and 0.4% silicon, between 0.05% and 0.15% molybdenum, up to 0.04% carbon, up to 0.01% and 0.03 phosphorus, between 0.005% and 0.007% sulfur and between 0.0001% and 0.05% of at least one rare earth selected from the group consisting of cerium, praseodymium and neodymium.

References Cited in the file of this patent UNITED STATES PATENTS 2,553,330 Post et al May 15, 1951 2,683,663 Tisdale et al. July 13, 1954 2,989,453 Esselman et al June 20, 1961 2,999,059 Treshow Sept. 5, 1961 OTHER REFERENCES Reactor Handbook, vol. I, Materials, June 27, 1960, Interscience Publishers, Inc., N.Y., page 563. 

1. IN AN ATOMIC REACTOR A STRUCTURAL ELEMENT ADAPTED TO WTIHSTAND NEUTRON RADIATION AND CONSISTING ESSENTIALLY OF AN AUSTENITIC STEEL CONSISTING ESSENTIALLY OF IRON AND BETWEEN 17% AND 19% CHROMIUM, BETWEEN 7% AND 11% NICKEL, BETWEEN 0.3% AND 0.6% MAGANESE, BETWEEN 0.35% AND 0.4% SILICON, BETWEEN 0.0K% AND 0.15% MOLYBDENUM, BETWEEN 0.03% ANG 0.04% CARBON, BETWEEN 0.01% AND 0.02% PHOSPHORUS, BETWEEN 0.005% AND 0.007% SULFUR AND BETWEEN 0.001% AND 0.05% OF AT LEAST ONE RARE EARTH SELECTED FORM THE GROUP CONSISTING OF CERIUM, PRASEODYMIUM AND NEODYMIUM. 